Device and Method for Optically Sensing a Specimen with a Large Depth of Field

ABSTRACT

A device for optically sensing a specimen with a large depth of field has a lighting module which illuminates a zone of the specimen during a predetermined measurement period with a pattern whose phase is modified in time during the measurement period, generating a specimen light to which a corresponding time-variable phase is imparted. The device also includes a detection module having a space-resolving detection zone which records the specimen zone and has multiple recording pixels, two analysis channels which can be connected to the recording pixels, and an analysis unit is connected to both analysis channels. A control unit is provided which, during the measurement period, connects each recording pixel in synchrony with the phase of the detected specimen light to the two analysis channels, alternatively, in such a way that the detected specimen light is divided into two portions phased in relation to one another, and the analysis unit calculates an optical split-image of the specimen zone on the basis of the two phased portions supplied to the analysis channels.

The invention relates to a device and a method for optically sensing aspecimen. In particular, it relates to the field of so-called structuredillumination, in which the modulation depth of the optical imaging of anamplitude structure (such as a grating) is used as the criterion for thedepth of field. The image of the periodic structure is distinguished bythe frequency of the modulation and the phase position (image phase) ofthe modulation. Different projection scenarios can be obtained by aphase shift of the structure perpendicular to the optical axis. Forinstance, three phase images at 0°, 120° and 240° are required to beable to calculate a depth-discriminated optical section, as isdescribed, for example in M. A. A. Nil et al., “Method of obtainingoptical sectioning by using structured light in a conventionalmicroscope,” Optics Letters 22 (24) 1997, pp. 1905-1907. Thedisadvantage in this case is that several images must be successivelyrecorded, read out and calculated.

In order to be able to generate the images already at the detector tothe extent possible, so that a limitation of the dynamic range bynon-confocal background signals is prevented, it is proposed in DE10254139 A1 that components of the detection or specimen light having aphase shift with respect to one another be spatially subdivided. Thishas the disadvantage, however, that in case of a linear illumination,for instance, at least two detector rows must be provided.

Starting from this basis, the problem of the invention is to provide amethod or a device for optical sensing of a specimen with a large depthof field in which the disadvantages mentioned above can be avoided.

According to the invention, the problem is solved by a device foroptical sensing of a specimen with a large depth of field, with anillumination module that illuminates an area of the specimen during apredetermined measurement period with a pattern, the phase of which isvaried over time, whereby specimen light to which a correspondingtime-varying phase has been imparted is generated; a detection modulehaving a space-resolving detection area with several recording pixels,two analysis channels connectable to the recording pixels, as well as ananalysis unit connected to the two analysis channels; and with a controlunit that connects, during the measurement period, each recording pixelalternately to the two analysis channels synchronously with the phase ofthe detected specimen light, so that the detected specimen light issubdivided into two components having a phase shift with respect to oneanother, and is supplied to the two analysis channels, wherein theanalysis unit calculates an optical section image based on thecomponents supplied to the two analysis channels.

Due to the provision of two separate analysis channels and thepossibility of connecting the recording pixels alternately to the one orthe other analysis channel, the two phase components of the specimenlight can be sensed with the same recording pixels, so that the dynamicrange of the detector is not limited by non-confocal background light.

The specimen light can be produced from an interaction of the light fromthe illumination module with the specimen, in particular, the specimenlight can be fluorescent light, reflected light, luminescence light,scattered light and/or transmitted light.

The pattern with which the specimen is illuminated is a predeterminedintensity distribution of the illumination light; in particular, aperiodic pattern or a periodic intensity distribution such as asinusoidal distribution is generated. The time-variation of the phasesis also preferably performed in a periodic manner. Here as well, asinusoidal or cosinusoidal phase change can be performed.

The control unit can connect the recording pixels alternately to the twoanalysis channels in such a manner that the phase shift is 180° (π). Anoptimal result in the calculation of the sectional image is obtained inthis manner.

Each recording pixel can have two subpixels, of which one of thesubpixels is connectable only to one of the two analysis channels, andthe other only to the second analysis channel. In this manner, thedetection module can be easily realized.

The recording pixels can be arranged side by side along one extensiondirection. In particular, a linear detection area can be realized inthis way. This is of particular advantage if the illumination moduleilluminates the specimen linearly and the linear illumination isdeflected over the specimen transversely to the direction of extension,since the linearly illuminated specimen area is always recorded in thiscase by means of the detection area. This can be implementedparticularly easily with the device constructed as a laser scanningmicroscope, since the scanner for the deflection of the illuminationlight is generally also used to de-scan the specimen light.

More particularly, each of the analysis channels can be constructed as aseparate analysis electronic unit. A fast and exact phase-dependentsensing of the components of the specimen light thereby becomespossible.

For each recording pixel, each analysis channel can have an integratorthat sums the supplied components during the measurement period.

The analysis unit for calculating the optical sectional image canadditionally subtract the two (preferably summed-up) components from oneanother. Thus the detection module can carry out all essential(particularly time-intensive) analyses in hardware, so that the imagedata basically needs only to be displayed to generate the sectionalimage. It is of course possible to record several optical sections indifferent parts of the specimen and to create a correspondingthree-dimensional representation from them by known methods.

In case of a linear detection, the phase variation is preferablyperformed in the direction of linear detection.

The invented device for optical sensing of a specimen with large depthof field is constructed in particular is a microscope. The microscopecan be a laser scanning microscope.

According to the invention, a method for optical sensing of a specimenwith large depth of field is additionally provided, in which an area ofthe specimen is illuminated during a predetermined measuring period witha pattern whose phase is varied temporally during the measurement,whereby specimen light is generated, to which a correspondingtime-varying phase has been imparted, and in which the specimen area isdetected in a space-resolving matter during the measurement period, andthe detected specimen light is subdivided into two components having aphase shift with respect to one another, wherein an optical sectionalimage of the specimen area is calculated on the basis of the components.With this method, an optical sectional image can be obtained quickly andwith high accuracy.

It is particularly preferred if the detected specimen light issubdivided with a phase shift of 180°. Then very good results can beobtained.

Several recording pixels can-be provided in this method forspace-resolving detection, each recording pixel having two subpixels andone of the subpixels supplying the first of the two components and theother of the two subpixels, the second component.

Moreover a linear, space-resolving detection can be performed. In thiscase space-resolving line detectors can be used.

In this method a separate analysis electronic unit, comprising anintegrator for instance, which sums the supplied components in aspace-resolving manner over the measurement period, can additionally beprovided for each component. Thus, the essential (in particular, thetime-intensive) analysis for generating the optical section with a largedepth of field can be performed in hardware. Such hardware solutions canusually be operated with very high precision and more rapidly thancorresponding solutions implemented in software.

In particular, the two components can be subtracted from one another tocalculate the optical sectional image. One can thereby obtain thedesired conformal image information.

Additionally, the specimen can be linearly illuminated and the phase canbe varied in the direction of the linear illumination. If the linearillumination is scanned across the specimen, the entire specimen can besensed with only one linear position-resolved detection being necessary.

The invented method for depth-resolved optical sensing of the specimenis, in particular, a microscopy method. The microscopy method can be alaser scanning microscopy method.

The invention will be explained in detail below with reference to thedrawing. Shown are:

FIG. 1, a schematic view of one embodiment of the invented device foroptical sensing of the specimen with a large depth of field;

FIG. 2, an enlarged schematic representation of detection module 4 fromFIG. 1;

FIG. 3, a diagram representing the measurement signal as a function ofthe number of phase-variation periods of the illumination pattern; and

FIG. 4, an alternative embodiment of detection module 4 from FIG. 1.

In the embodiment shown in FIG. 1, the device for optical sensing of aspecimen with a large depth of field is constructed as a laser scanningmicroscope, which comprises an illumination module 1, a scanning module2, a microscope module 3, a detection module 4 and a control unit 5.

Illumination module 1 generates a laser beam that is directed toscanning module 2, which deflects the laser beam across specimen 7, viaa beam splitter 6 inserted between illumination module 1 and scanningmodule 2. Illumination module 1 is constructed here such that the laserbeam is linearly focused on, or preferably in, specimen 7, with the lineextending perpendicular to the plane of the drawing. Scanning module 2produces a deflection of this linear focus in a direction Aperpendicular to the extension direction of the linear focus, so thatthe entire specimen is illuminated.

Illumination module 1 comprises a laser source 8 for generating a laserbeam, optics 9 downstream of laser source 8 to produce the linearfocusing, as well as a transmissive amplitude grating 10 which impartsan intensity distribution to the laser beam along the extensiondirection of the linear focus. This intensity distribution is preferablya periodic intensity distribution, e.g., a cosinusoidal distribution.During operation of the device, amplitude grating 10 is additionallymoved rapidly back and forth in the extension direction of the linearfocus (i.e., perpendicular to the plane of the drawing in this case), sothat a time-varying phase is additionally imparted to the intensitydistribution. The back-and-forth motion of amplitude grating 10 isselected such that it is markedly faster than the deflection by means ofscanning module 2 so that each linearly illuminated section of specimen7 is illuminated with a pattern (intensity distribution of amplitudegrating 10) whose phase varies over time. For instance, theback-and-forth movement can be sufficiently fast that each linearlyilluminated section is illuminated during more than 20, more than 100,or more than 1000 periods of the back-and-forth motion.

In its focus, the focused laser beam brings about the generation ofspecimen radiation which reaches scanning module 2 via microscope module3, so that the specimen radiation is present downstream of the scanningmodule (i.e., between scanning module 2 and beam splitter 6), as astationary beam. It is therefore often said that scanning module 2de-scans the specimen radiation. Beam splitter 6 is constructed totransmit the specimen radiation in such a manner that the latter strikesdetection module 4.

Detection module 4 comprises, as shown in FIG. 2, a space-resolving,linear detection area 11 with several recording pixels 12. To simplifythe illustration only two recording pixels 12 are shown. Of course, thenumber of recording pixels can be much larger, e.g., 512 or 1024recording pixels.

Despite the naturally occurring three-dimensional illumination of thespecimen, only the plane (optical section) that lies in the focal planeof microscope module 3 can be reproduced by the phase-dependent analysisof the specimen light described below. If one records several sectionsin different depths of the specimen, a three-dimensional image of thespecimen can subsequently be calculated with known methods.

For phase-dependent analysis of the specimen light, analysis channels 13and 14 are on either of the linearly arranged recording pixels 12,analysis channel 13 sensing the in-phase component of the specimenlight, and analysis channel 14 sensing the out-of-phase component of thespecimen light. Due to the back-and-forth motion of phase grating 10,the individual points inside the illuminated line in the specimen aresometimes illuminated with maximum intensity and sometimes with minimumintensity. The specimen light that comes from the points illuminatedwith maximum intensity corresponds to the in-phase component, while thespecimen light coming from those points which are illuminated withminimum intensity corresponds to the out-of-phase component.

The association of minimum or maximum intensity with out-of-phase andin-phase components applies in the strict sense only if the intensitydistribution of the pattern is rectangular. In the case of acosinusoidal distribution, for instance, one can determine a thresholdvalue, with specimen light originating from points that are illuminatedwith an intensity greater than the threshold value corresponding to thein-phase component. On the other hand, specimen light originating frompoints that are illuminated with an intensity that is not greater thanthe threshold value corresponds to the out-of-phase component.

One can also say that the in-phase component here corresponds to thesignal from the confocal section plus a background signal multiplied bythe in-phase component of detection area 11. The in-phase component ofdetection area 11 corresponds to the grating formed by the recordingpixels 12 that are connected to first channel 13. In the same manner,the out-of-phase component carries the signal from outside the confocalsection image plus the background signal multiplied by the out-of-phasecomponent of detection area 11. The out-of-phase component of detectionarea 11 corresponds to the grating formed by the recording pixels 12that are connected to second analysis channel 14.

The two analysis channels 13 and 14, respectively, integrate or sum thein-phase component and the out-of-phase component for each recordingpixel 12 over the dwell time of the linear focus at one point of thespecimen. The integrated individual signals for each recording pixel 12are subsequently subtracted from one another and yield the integratedmeasurement signal S. For a sufficiently large number of back-and-forthmovements, it can be deduced for a cosinusoidal intensity distributionof the linear focus, for instance, that the measurement signal S(P)corresponds to half the signal from the optical sectional image. Thissignal no longer contains the undesired background signals from planesthat lie outside the focus. A corresponding derivation of thisrelationship can be derived from DE 10254139 A1, wherein the in-phaseand out-of-phase components from detection area 11 correspond to thein-phase and out-of-phase components of the structure ST. FIG. 3schematically shows how measurement signal S approximates thehalf-signal value A/2 as a function of the number of periods P ofback-and-forth movement.

In the detection area 11 shown in FIG. 2, each recording pixel 12 isconstructed of two subpixels 15, 16 arranged side by side. Depending onwhether the in-phase component or the out-of-phase component strikespixel 12, either subpixel 15 is connected via a transfer gate 17 to anintegrator 18 of the first analysis channel 13, or subpixel 16 isconnected via a transfer gate 19 to an integrator 20 of second analysischannel 14.

At a first point in time, subpixel 15 of the right recording pixel 12 inFIG. 2 is thus connected to first analysis channel 13 and subpixel 16 ofthe left recording pixel 12 is connected to second analysis channel 14(hatched arrows P1, P2). At a second point in time, however, subpixel 16of the right recording pixel 12 is connected to second analysis channel14 and subpixel 15 of the left recording pixel 12 is connected to firstanalysis channel 13 (arrows P3, P4).

Thus, a splitting of the in-phase component and the out-of-phasecomponents of the specimen line is brought about by selective connectionof analysis pixel 12 to first or second analysis channel 13, 14. Afterall periods of the backward and forward motion of amplitude grating 10have been completed, the in-phase and out-of-phase measurement signalsof integrators 18, 20 generated for recording pixel 12 are supplied viacorresponding shift registers 21, 22 to a subtractor 23 (arrows P5, P6,P7, P8, P9, P10), which subtracts the out-of-phase component from thein-phase component for each recording pixel and thus generates thedesired measurement signals S. The desired sectional image can then begenerated or calculated from measurement signals S.

Subpixels 15 and 16 of the individual recording pixels 12 naturally neednot be arranged side by side as shown in FIG. 2. They can also bearranged one above the other.

The measurement process described here (including the scanningillumination) is controlled by means of control unit 5.

A modification of recording module 4 shown in FIG. 2 is represented inFIG. 4. Recording module 4 in FIG. 4 differs from that shown in FIG. 2in the construction of detection area 11. In detection area 11 of FIG.4, each recording pixel is constructed from one pixel that can beselectively connected to first or second analysis channel 13, 14. At afirst point in time therefore, the first and third analysis pixels 12(from the left in FIG. 4) can be connected to analysis channel 13 andthe second and fourth analysis pixels 12 can be connected to secondanalysis channel 14 (hatched arrows P11). At a second point in time, theconnection of recording pixels 12 to the analysis channels is reversed(arrow P12). After expiration of the measurement period, the summedin-phase and out-of-phase components in integrators 18, 20 are againsupplied via shift registers 21, 22 to subtractor 23, which generatesthe measurement signals S for recording pixels 12. Unlike theconstruction in FIG. 2, the specimen light is used completely becauseall recording pixels 12 are always connected either to the first or thesecond recording analysis channel 13, 14. The resolution is also higherin comparison with the embodiment of FIG. 2, since all pixels alwayscontribute to the image generation.

1. A device for optical sensing a specimen with a large depth of field,an illumination module that illuminates an area of the specimen during apredetermined measurement period with a pattern, the phase of whichvaries over time during the measurement period, generating a specimenlight, to which a corresponding time-varying phase is imparted, isgenerated, a detection module having a space-resolving detection areawith multiple recording pixels, two analysis channels connectable torecording pixels, and an analysis unit connected to the two analysischannels, and a control unit that alternately connects each recordingpixel in temporal synchronism with the phase of the detected specimenlight to the two analysis channels during the measurement period, sothat the detected specimen light is subdivided into two componentshaving a phase shift with respect to one another, and is supplied to theanalysis channels, wherein the analysis unit calculates an opticalsectional image of the specimen area based on the components supplied tothe analysis channels.
 2. The device according to claim 1, in which thecontrol unit connects each recording pixel alternately to the twoanalysis channels such that the phase shift amounts to 180°.
 3. Thedevice according to claim 1, in which each recording pixel has twosubpixels, wherein one of subpixels can be connected only to the firstof the two analysis channels and the other subpixel can be connectedonly to the second analysis channel.
 4. The device according to claim 1,in which the recording pixels are arranged side by side along anextension direction.
 5. The device according to claim 1, in which eachof the analysis channels is constructed as a separate analysiselectronic unit.
 6. The device according to claim 1, in which eachanalysis channel for each recording pixel has an integrator that sumsthe supplied components during the measurement period.
 7. The deviceaccording to claim 1, in which the analysis unit subtracts the twocomponents from one another to calculate the optical sectional image. 8.The device according to claim 1, in which said illumination moduleilluminates the specimen linearly and varies the phase in the directionof the linear illumination.
 9. A method for optical sensing of aspecimen with large depth of field, in which an area of the specimen isilluminated during a predetermined measurement period with a pattern,the phase of which is temporally varied during the measurement period,generating a specimen light, to which a corresponding time-varying phaseis imparted, and in which the specimen area is detected during themeasurement period in a space-resolving manner and the detected specimenlight is subdivided into two components having a phase shift withrespect to one another, wherein an optical sectional image of thespecimen area is calculated based on the components supplied to theanalysis channels.
 10. The method according to claim 9, in which thedetected specimen light is subdivided with a phase shift of 180°. 11.The method according to claim 9, in which several recording pixels areprovided for space-resolving detection wherein each recording pixel (12)has two subpixels (15, 16) and one of the subpixels (15, 16) suppliesonly the first of the two components, and the other subpixel suppliesonly the second component.
 12. The method according to claim 9, in whicha linear, space-resolving detection is performed.
 13. The methodaccording to claim 9, in which a separate analysis electronic unit isprovided for each component.
 14. The method according to claim 9, inwhich an integrator that sums up the supplied components over themeasurement period in a space-resolving manner is provided for eachcomponent.
 15. The method according to claim 9, in which the twocomponents are subtracted from one another to calculate the opticalsectional image.
 16. The method according to claim 9, in which thespecimen is illuminated linearly and the phase is varied in thedirection of the linear illumination.